This invention relates to a cahtode ray display tube having an envelope with a subtantially planar faceplate carrying a phosphor screen, a channel plate electron multiplier disposed substantially parallel to, and spaced from, the screen, the channel electron multiplier having an input side over which, in use of the tube, an electron beam is scanned and an output side facing the screen from which a current multiplied electron beam is directed onto the screen.
The invention is concerned especially, but not exclusively, with a so-called "flat" cathode ray display tube generally of the kind described in published British Patent Application No. 2101396A, corresponding to U.S. patent application Ser. No. 830,388, filed Feb. 14, 1986. With this kind of display tube, a low energy electron beam is directed along a path parallel to the screen and is turned through 180.degree. so that it then travels in the opposite direction. The beam is subsequently deflected onto the input side of the channel plate multiplier where it undergoes electron multiplication before being accelerated onto the screen to excite the phosphor material by a field established between the output of the multiplier and a screen electrode. With such an arrangement, a compact, flat tube is achieved.
In one realised version of this flat tube, the electron multiplier comprises a glass micro-channel plate multiplier formed with thousands of individual channels extending therethrough. It is important for optimum operation of the display tube that the channel plate multiplier be maintained accurately parallel to, and in predetermined spatial relationship with, the planar faceplate, and thus the screen.
Heretofore, the multiplier has been held rigidly clamped relative to the screen. However, being formed of thin glass (around 1 mm), the multiplier is comparatively fragile and there is a risk with this kind of rigid clamping that the multiplier may fracture during assembly, particularly if its surfaces or those of the clamping elements are not precisely even, for example if one or both of the multiplier's input and output surfaces have small undulations. Moreover, there is a risk also that the multiplier can be damaged as a result of the tube being subjected to mechanical shock or vibration or as a result of differences in thermal expansion rates of the multiplier and the clamping arrangement. An object of the present invention is to overcome to some extent the above mentioned problems.